While the Yes campaign continued to insist publicly that Salmond won the debate, many senior figures were telling a different story privately.

The First Minister has benefited from the loyalty of staff and fellow SNP politicians.

But yesterday there was unprecedented criticism of how he had performed in the most important day in the independence debate to date.

One senior source said: “It’s not as if the currency issue is new. The Fiscal Commission reported 18 months ago and there has been a lot of time to think about a response.

“A lot of time has gone into thinking about how to answer those questions and it just didn’t happen on the night.

“There is a good case to be made on currency but he didn’t make it.”

Asked if Salmond could have been under-prepared for the debate because of his commitments at the Commonwealth Games and the World War I Memorial, the source said: “No. He is the First Minister, this is something he has been preparing for.

“It’s not as if we didn’t know the currency issue was something Darling would bring up and spend a lot of time on. Hours and hours were set aside to perfect responses to those questions.”

There was also criticism of the questions Salmond asked Darling.

Observers were astonished when he used a large part of precious TV time to ask Darling about claims that Scots would have to drive on the right-hand side of the road if there was a Yes vote.

He also asked about bizarre claims Scotland would be more vulnerable to attacks from outer space.

The source said: “Those questions ate up an awful lot of time and were a wasted opportunity.

“People make mistakes but he didn’t do as well as he should have done. It didn’t go well.”

Other sources, including MSPs, were also critical of Salmond’s performance.

One said: “It was a bad night.”

Another added: “It was what it was. Now we have to pick ourselves up and prepare for the next one.”

Asked if the debate was “a bit of a disaster”, one MSP echoed a famous quote from 90s TV show House of Cards. “You may say that,” the source said. “I couldn’t possibly comment.”

Figures in the Yes campaign also criticised Salmond’s handling of the currency issue. Former SNP deputy leader Jim Sillars said: “I’ve been warning Salmond for months that his position on the pound is stupid.”

But Sillars – the widower of legendary Nationalist Margo MacDonald – insisted the referendum could still be won.

He added: “Luckily, I and others are out making the case to Scots people that we can use our own currency pegged to the pound.”

Scottish Tory MSP Murdo Fraser seized on the unhappiness in the SNP camp.

He claimed many Nationalists were talking about ditching Salmond and putting Sturgeon up for the next debate, on the BBC.

But his comment was dismissed by an SNP spokesman as “silly Tory nonsense”.

Salmond has already vowed to fight on as First Minister – even if voters reject his vision for independence.

His pledge – made two months ago – shocked many at Holyrood who expected him to make way for Sturgeon in the event of a No vote.

Sturgeon has made no secret of her desire to take the top job in Scottish politics.

In March, she told the Record: “Anybody, in any walk of life, if they are ambitious, wants to get to the pinnacle of their profession.

“So, hypothetically of course, that is something I would like to think that one day I will get the chance to do.

“Will I ever get the chance to do it? Well, that is not ultimately up to me.”

If Salmond loses the referendum and resigns, Sturgeon could be sworn in as SNP leader – and potentially First Minister – within a matter of weeks.

Salmond yesterday put on a brave face as he met with pro-independence business owners.

He insisted the Scottish Government’s position on currency is now totally clear.

Salmond said: “The first thing you have to do in a currency debate is establish what your policy is and nobody can be in any doubt that the Scottish Government’s policy is to keep the pound.

“Why? Because it’s our pound – it’s not George Osborne’s or Alistair Darling’s.

“We can’t be dictated to – it’s part of the assets of this country to which we should be entitled to keep. If the sovereign will of the Scottish people in a referendum says that’s what we do then that’s what will happen.”

But he changed tack from the debate by admitting keeping the pound without a formal currency union is “quite attractive”.

He added: “It also tells you why it ain’t going to happen. No UK Chancellor would allow himself to be in a position where an independent Scotland gets away scot-free without the debt. We will take our share of assets in return for our share of the liabilities.”